Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $44.95   8.859%   $48.9321   $48.93   $48.95   $48.90  
  Purchase #2 $161.65   10.749%   $179.0258   $179.03   $179.05   $179.00  
  Purchase #3 $208.29   6.469%   $221.7643   $221.76   $221.75   $221.80  
  Purchase #4 $24.47   6.128%   $25.9695   $25.97   $25.95   $26.00  
  Purchase #5 $122.36   9.583%   $134.0858   $134.09   $134.10   $134.10  
  Purchase #6 $20.86   5.413%   $21.9892   $21.99   $22.00   $22.00  
  Purchase #7 $186.33   8.308%   $201.8103   $201.81   $201.80   $201.80  
  7 purchase totals = $768.91       $833.5770   $833.58   $833.60   $833.60